Gypsum crystals (CaSO4) found within the littoral zone of Lake Chichancanab

Because the water of Chichancanab is nearly saturated with CaSO4

, gypsum crystals can be found in the littoral zone encrusting aquatic macrophytes. However, gypsum is not precipitating in the
open lake today. This image illustrates gypsum crystals found at depth in the sediment core taken in 6.9 m of water. The presence of gypsum in the littoral zone indicates times in the past when the climate was drier, the lake volume was reduced, and
gypsum was precipitating from lake water. We can therefore use the sulfur content of the lake sediments, which reflects gypsum content (CaSO4

), as an indicator of dry climatic conditions.

Photo Credits:
David A. Hodell
Department of Geology, University of Florida